Of all the strange aircraft the United States built during the Second World War — and there were many — none was stranger, on paper or in person, than the Northrop XP-79.

The XP-79 was, in concept, a manned missile. Its mission was not to shoot down enemy bombers with guns or rockets. Its mission was to physically ram them. The aircraft was designed around a magnesium-alloy leading edge thick enough to slice through an enemy fuselage in mid-air, while the XP-79 itself, sturdier than the bomber it had just gutted, would, theoretically, fly home for another go.

It was the kind of idea that could only have been entertained in a war so total that the U.S. Army Air Forces seriously contemplated buying a fighter whose entire combat doctrine was a mid-air collision. Northrop signed the contract. The aircraft was built. It flew once.

Why anyone thought this was a good idea

To understand the XP-79 you have to understand 1942. The German Luftwaffe was bombing England with Heinkel He 111s and Junkers Ju 88s. The U.S. Army Air Forces, having watched the Royal Air Force lose dozens of fighters in single missions over the previous two years, was looking for radically new ways to defeat heavy bombers. One school of thought, championed by a few engineers and a smaller group of generals, said the answer was a fighter that did not need ammunition. A fighter that did its work with structural strength, not bullets, would be cheaper to operate and would never run out.

The Northrop Corporation, founded by the visionary engineer Jack Northrop, had been working on flying-wing designs since the 1930s. Northrop’s company already had a pure flying-wing demonstrator — the N-1M — and a clear theoretical understanding of how to build a tailless aircraft that could survive aerodynamic loads other fighters could not. When the USAAF asked for a flying ram, Northrop was, almost uniquely, in a position to design one.

A fighter you flew lying down

The XP-79 was, by any measure, a peculiar aircraft. The pilot did not sit in a normal seat. He lay flat on his stomach, head forward, in a prone-pilot cockpit cut into the centre of the wing. The reasoning was high-G tolerance: a pilot lying down can withstand significantly more positive G-load before greying out than a pilot sitting up. For a fighter that was supposed to ram bombers, the design team expected sudden manoeuvres on the order of nine or ten G. The prone position was the only way to keep a human conscious through the actual impact.

The aircraft itself was a low-aspect-ratio flying wing built almost entirely of welded magnesium alloy. The thickness of the leading edge — over twenty centimetres in places — was deliberate. It was designed to bite through aluminium bomber fuselages without itself breaking. The two Westinghouse 19B turbojets gave the aircraft a planned top speed of around 870 km/h, faster than any contemporary German bomber. Four .50-calibre machine guns were added to the armament late in development as a concession to USAAF pilots who, predictably, balked at the idea of having no defensive weapons at all.

The single flight

The XP-79B — the only example built — sat in the desert at Muroc Army Air Field (later Edwards Air Force Base) for most of 1945, undergoing taxi tests, ground runs, and structural inspections. By September the war had been over for nearly a month. The Japanese had surrendered. The XP-79’s stated mission — ramming German bombers over Europe — had been moot for the better part of the year.

Northrop and the USAAF flew it anyway, partly out of contractual obligation and partly because the data on prone-pilot cockpits and flying-wing aerodynamics was considered valuable.

The first flight, on 12 September 1945, was given to test pilot Harry Crosby. He took off normally. He climbed to several thousand feet and began a low-rate roll to assess control authority around the longitudinal axis. About fifteen minutes into the flight, the aircraft entered an uncommanded descent. Crosby fought it for some seconds, then attempted to bail out. He was struck by the aircraft as he left the cockpit and fell to his death. The XP-79B crashed and burned in the desert.

The programme was cancelled within weeks.

Why this aircraft still matters

Most readers will, reasonably, file the XP-79 under “Second World War oddities” and move on. That would be a mistake. Three things from the XP-79 programme survived its violent end.

The first is the prone-pilot cockpit. Northrop’s data from the XP-79 directly informed later high-G aircraft research, including the prone-pilot Reid and Sigrist Bobsleigh in Britain and post-war centrifuge testing of pilot G-tolerance. The reclining seat in the F-16, the F-22, and every modern fighter is a distant descendant of the lessons learned in 1945.

The second is the flying-wing aerodynamic data. Jack Northrop’s company carried that knowledge through the YB-35 and YB-49 of the late 1940s, the unsuccessful but influential N-9M demonstrator series, and eventually — many decades later — into the B-2 Spirit and the B-21 Raider. The XP-79 was a stepping stone in a programme of flying-wing research that ultimately produced the most successful stealth bomber in history.

The third is the magnesium-alloy structural research. Magnesium-aluminium alloys are now used routinely in aerospace structures, particularly in helicopter gearboxes and certain fighter components. The XP-79’s all-magnesium airframe was an early proof that the metal could be welded, formed, and stressed in load-bearing applications.

An aircraft from a more desperate decade

It is impossible to look at photographs of the XP-79 — squat, heavy-leading-edged, with its peculiar slot windows for the prone pilot — without thinking about the world that built it. A world in which the United States was at the same time developing the atomic bomb, building 300,000 aircraft, and entertaining a serious proposal for a flying ram. The XP-79 was, in a sense, the spirit of the era distilled into a single airframe.

It also reminds us that not every aviation idea is a good one. Sometimes the most valuable lesson is what does not work — and Harry Crosby paid the price for that lesson on a clear September morning in 1945.

Sources: U.S. Air Force Test Center History, National Air and Space Museum, Northrop Grumman corporate archive.